by Les Saidel - July, 2011
How does bread rise? This could be a one word article - yeast! Unfortunately, despite yeast's primary role in the rising effect of the bread, it is, by far, not the only factor involved. So, sit back and read on.
In this article I am going to explain all the components that contribute to the rising of bread and reveal some tricks of the trade that you can use in your own baking to make your bread rise higher and get a plumper, fuller loaf or challah.
The process of bread rising is biotechnology at its finest. We read in science magazines about the latest, cutting-edge research - scientists using living cells to produce supercomputers and physiologists using other biotechnologies to find cures for cancer, AIDS, etc. It may seem that we are living in a "new" era of exploration with wonderful discoveries and revelations just around the corner, but this is not completely true.
Man has been using biotechnology for centuries, even millenia. Even though he did not fully understand its workings, he has used it successfully to bake bread since the dawn of time. This is biotechnology at its finest - using a living organism to perform a specific technical task that is beneficial to mankind.
Only in the last 400 hundred years or so, starting with Dutch scientist Antony van Leeuwenhoek who invented the microscope and Louis Pasteur who discovered and classified bacteria, has our understanding of this process deepened.
Basically, without going into too many chemical details, the yeast cells feed on glucose (from broken down starch in the flour) and produce acids (acetic and lactic) and carbon dioxide (CO2). As the yeast eat and multiply, so does their CO2 production increase. It is these expanding bubbles of CO2 which cause the dough to rise. However, that is only part of the story.
It is one thing to have a gas producer, the yeast, but if you do not have a framework in which these gas bubbles will be trapped (like in a balloon), they will simply dissipate into the air and do nothing. This network of small balloons is in fact the gluten network in the dough.
Bread flour contains both starch and protein (and if it is whole wheat flour - another plethora of vitamins and minerals). The starch is broken down into glucose and serves as food for the yeast. The protein content of the flour is what creates the gluten structure of the dough.
Actually there are two specific proteins - gliadin and glutenin, which combine to become gluten. Each one contributes a special property to the dough. Gliadin makes the dough more elastic (the property that makes it retract) and glutenin makes it more extensible (it can be stretched without tearing).
In order for these proteins to work their magic, they must be vigorously combined and mixed together. This is achieved by the process of kneading.
Correct kneading consists of two distinct stages - incorporation and building the gluten structure. In the incorporation stage, the purpose is simply to mix all the ingredients until they are uniformly dispersed in the dough. When this is completed, the dough is not yet ready. Many make the mistake in thinking that this is sufficient to create a high quality dough, but it is not.
After the incorporation stage comes the kneading stage. This process involves a stretching and folding of the dough, numerous times. This stretching and folding is the process that combines the gliadin and glutenin into the gluten network required. It may be achieved by an electric mixer or by hand.
The best way to determine when the gluten structure is fully developed is to do the "windowpane test". Simply take a small ball of dough and stretch it between your fingers to as thin a membrane as you can without it tearing. The more developed the gluten structure in the dough, the thinner and more translucent the membrane will be.
All doughs are different, but a simple rule of thumb is that a dough needs at least 15 minutes of hand kneading or 8-10 minutes of machine kneading on medium speed to achieve full gluten development.
In correctly developing the gluten, you create an intricate spider's web of gluten fibres which act as balloons around the CO2 gas bubbles produced by the yeast cells. The stronger the balloon, or the gluten structure, the more it can be inflated before it pops and the higher your bread will rise.
The first mixing or kneading of a dough (unless a high powered industrial mixer is used), is still insufficient to achieve full gluten development. To reach this stage we need to leave the dough to rise for a time (depending on the amount and type of yeast used) before the dough is shaped into its final form. This is called the first or primary rise. After this rise (usually when the dough has doubled or more in size), it is punched back, i.e use your fist to punch the middle of the dough in and deflate it. Then gather the dough from the periphery of the bowl and twist it in toward the center. French bakers call this - giving the dough a "turn".
This turning or "punching back" achieves two purposes - it deflates the dough and removes excess CO2 which inhibits further proliferation of the yeast cells, and it further stretches and folds the dough, thus strengthening the gluten structure even more. You will notice that after the punch back, if the dough were allowed to rise again, it would do so at double the previous rate. This is because there are more yeast cells to produce CO2 and the gluten structure is now stronger and can be inflated more.
The next stage is to shape the bread/challah and leave it to rise again - the second rise.
This is the most difficult part of the dough development because it is dependent on a large number of factors, humidity, room temperature being but a few. Even experienced bakers goof this stage because they are not paying enough attention. It is at this stage that the dough needs to be "babysitted". You need to continually watch it, and more accurately - prod it with your finger - to determine if it has reached the required level of rising or not.
Lightly prod the dough with your finger. If the dough immediately bounces back and there is no trace of indentation - then the dough has not risen enough and if you bake it now, it will either tear during the bake and/or will not have a light fluffy crumb. If the prodding causes an indentation that does not bounce back at all and even causes the entire dough to sag - you have left it too long and if you bake it now the bread will sag or "flop" during the bake. The correct situation is when the prod causes a slight indentation but one that also bounces back slightly. This is a "ready" dough. You will learn this stage from experience and much prodding.
A dough which has reached the correct second rising stage has not yet fully risen to its limit - it still has some way to go. This is the right stage to place it in the oven - as it will rise more during the bake. If the dough has been left to rise to its limit, it will have no "play" left and will sag during the bake.
The final factor in getting a fully developed loaf is the oven temperature. If too low, the bread will not experience "oven spring" - i.e it will not rise more during the bake. If too high, the crust will harden before it has risen sufficiently and will again not rise enough in the oven. You should experiment with different temperatures to see which works best. Also remember - all ovens are not created equally - you need to learn your oven's behaviour. A general rule of thumb though is to rather have the oven hotter than too low.
A loaf that has sufficient yeast, has its gluten fully developed, is left to rise twice with a punch-back and is baked at just the right time at the right temperature, will be a perfect loaf - in appearance and texture at least. As for taste - that's another article alltogether.
It sounds complicated and the truth is - it is a little. To bake a loaf of bread is dead easy. To bake a GREAT loaf of bread - now that takes a little more work!
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